Move monkeypatching of metadata 2.0 support to a more proper place

It was done in the support code for the wheel file format but it
affects metadata loading from all supported distribution types. Move
it to generic code.

twine/package.py

@@ -27,6 +27,18 @@
 from twine import sdist
 from twine import wheel
 
+# Monkeypatch Metadata 2.0 support
+metadata._VALID_METADATA_VERSIONS = [
+    "1.0",
+    "1.1",
+    "1.2",
+    "2.0",
+    "2.1",
+    "2.2",
+    "2.3",
+    "2.4",
+]
+
 DIST_TYPES = {
     "bdist_wheel": wheel.Wheel,
     "sdist": sdist.SDist,

twine/wheel.py

@@ -16,15 +16,9 @@
 import zipfile
 from typing import List
 
-import packaging.metadata
-
 from twine import distribution
 from twine import exceptions
 
-# Monkeypatch Metadata 2.0 support
-packaging.metadata._VALID_METADATA_VERSIONS = ["1.0", "1.1", "1.2", "2.0", "2.1", "2.2", "2.3", "2.4"]
-
-
 wheel_file_re = re.compile(
     r"""^(?P<namever>(?P<name>.+?)(-(?P<ver>\d.+?))?)
         ((-(?P<build>\d.*?))?-(?P<pyver>.+?)-(?P<abi>.+?)-(?P<plat>.+?)